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C HAPTER
685
23
MS From Populations to the
Biosphere
C HAPTER O UTLINE
23.1 I NTRODUCTION TO E COLOGY
23.2 P OPULATIONS
23.3 C OMMUNITIES
23.4 E COSYSTEMS
23.5 B IOMES AND THE B IOSPHERE
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Observe the cheetah hunting its prey. What is it called when one organism hunts another organism? Predation.
Predation may not be good for the survival of an individual organism, but it is a very important part of life. This is
because every interaction between an organism affects other organisms in an ecosystem.
What other things do you notice about the image? Where is the cheetah hunting? How do you think the cheetah has
adapted to live in that particular environment? What do you think the weather is like? Does it rain a lot? Are there
bigger trees? Or just small grasses?
All of the living and non-living things and how they interact with each other make up an ecosystem. The study of
these interactions is called ecology. Ecologists ask questions like, "What would happen if the cheetahs’ prey goes
extinct?" and, "What would happen if a fire wiped out the grasslands where cheetahs live?"
Think about other interactions between organisms you have observed. Maybe you have seen a bee sucking the nectar
out of a flower, or a cow grazing on grass. What habitats do these organisms live in? How do humans affect their
habitats?
All of these questions are ecological questions. Think about them as you read the following chapter.
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Introduction to Ecology
Lesson Objectives
• Define ecology.
• Describe how organisms can interact with their environments.
• Describe levels of organization in ecology.
Check Your Understanding
• What is an adaptation?
• What is the scientific method?
Vocabulary
abiotic Physical (nonliving) properties of an organism’s environment, such as sunlight, climate, soil, water and air.
biome A large community of plants and animals that live in the same place.
biosphere The part of the planet and atmosphere with living organisms.
biotic Biological (living) properties of an environment, i.e., the living organisms in a habitat.
community Populations of different species that occupy the same area and interact with each other.
ecology The scientific study of how living organisms interact with each other and with their environment.
ecosystem A natural unit composed of all the living forms in an area, functioning together with all the abiotic
components of the environment.
What is Ecology?
Life Science can be studied at many different levels. You can study small things like molecules or cells. Or you can
study big things like whole organisms or groups of organisms. The largest level that you can study is the level of
ecology. Ecology is the study of how living organisms interact with each other and with their environment.
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Because it is such a large field, ecology involves many different fields, including geology, soil science, geography,
meteorology, genetics, chemistry, and physics. You can also divide ecology into the study of different organisms,
such as animal ecology, plant ecology, insect ecology, and so on.
A biome is a large community of plants and animals that live in the same place. Ecologists can also study biomes.
For example, ecologists can study the Arctic, the tropics, or the desert (Figure 23.1 ). Can you think of different
species or biomes that ecologists could study?
FIGURE 23.1
An example of a biome the Atacama
Desert in Chile.
Ecologists do two types of research:
a. Field studies.
b. Laboratory studies.
Field studies involve collecting data outside in the natural world. An ecologist who completes a field study may
travel to a tropical rain forest and count all of the insects that live in a certain area. Laboratory studies involve
working inside, not in the natural world. Sometimes, ecologists collect data from the field, and then analyze it in the
lab. Also, they use computer programs to predict what will happen to organisms in who live in a specific area. For
example, they may make predictions about what happens to insects in the rainforest after a fire.
Organisms and Environments
All organisms have the ability to grow and reproduce. To grow and reproduce, organisms must get materials and
energy from the environment.
An organism’s environment includes two types of factors:
a. Abiotic factors are the parts of the environment that have never been alive, such as sunlight, climate, soil,
water and air.
b. Biotic factors are the parts of the environment that are alive, or were alive and then died, such as plants,
animals, and their remains.
Biotic factors, like organisms, interact with abiotic factors. For example, all animals (biotic factors) breathe in
oxygen (abiotic factor). All plants (biotic factor) absorb carbon dioxide (abiotic factor).
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Can you think of another way that abiotic and biotic factors interact with each other?
Levels of Organization in Ecology
Ecology can be studied at small levels or at large levels. Levels of organization are described below from the largest
to the smallest:
• The biosphere is the part of the planet that has living things on it (Figure 23.2 and Table 23.1 ). This is most
of Earth.
• An ecosystem is the living things in an area interacting with all of the abiotic parts of the environment (Figure
23.3 ).
• A community are all of the populations of different species that live in the same area and interact with one
another.
• A population is a group of organisms belonging to the same species that live in the same area and interact with
one another.
FIGURE 23.2
The global biosphere which includes all
areas that contain life from the sea to
the atmosphere.
TABLE 23.1: Ecological Range
Level
population
community
ecosystem
biosphere
Definition
organisms belonging to the same species that live in the
same area and interact with one another
populations of different species that live in the same
area and interact with one another
a natural unit composed of all the living forms in an
area, interacting with all the abiotic components of the
environment
the part of the planet that has living things
Ecologists study ecosystems at every level. They can ask different types of questions at each level. Examples of
these questions are given in Table 23.2 , using the zebra as an example.
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FIGURE 23.3
Satellite image of Australia&#8217 s
Great Barrier Reef an example of a marine ecosystem
TABLE 23.2: Ecological Ecosystems
Level
Individual
Population
Community
Ecosystem
Biosphere
Question
How do zebras keep water in their bodies?
What causes the growth of a zebra populations?
How does a disturbance, like a fire or predator, affect
the number of mammal species in African grasslands?
How does fire affect the amount of food available in
grassland ecosystems?
How does carbon dioxide in the air affect global temperature?
Lesson Summary
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•
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Ecology is the scientific study of how living organisms interact with each other and with their environment.
The study of ecology can be broken down into different fields and studied in the field or in the lab.
An organism’s environment includes abiotic and biotic factors.
Levels of organization in ecology include the population, community, ecosystem and biosphere.
Review Questions
Recall
1. Name three fields you can study when you study ecology.
2. Define ecosystem.
3. Define organism.
4. What are the four main levels of organization in ecology?
Apply Concepts
23.1. INTRODUCTION TO ECOLOGY
5. What is the difference between field studies and laboratory studies?
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Further Reading / Supplemental Links
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http://www.ecokids.ca/pub/index.cfm
http://www.eco-pros.com/ecologykids.htm
http://www.kidsolr.com/science/page12.html
http://www.southplainfield.lib.nj.us/homeworklinks/Ecology.htm
http://www.surfnetkids.com/ecology.htm;
http://en.wikipedia.org/wiki
Points to Consider
• What do you think causes populations to grow?
• What causes populations to decrease?
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23.2
Populations
Lesson Objectives
•
•
•
•
•
Define population.
Describe how births, deaths and migration affect population size.
Explain how populations grow.
Describe how limiting factors affect population growth.
Describe growth of the human population.
Check Your Understanding
• What is ecology?
• How does an organism interact with its environment?
Vocabulary
birth rate Number of births per individual within the population per unit time.
carrying capacity Maximum population size that can be supported in a particular area without degradation of the
habitat.
death rate Number of deaths within the population per unit time.
dispersion The spacing of individuals within a population.
emigration Movement of individuals out of a population.
immigration Movement of individuals into a population from other areas.
limiting factor A living or nonliving property of a population’s environment, which regulates population growth.
population growth rate How the population size changes per unit of time.
What is a Population?
A population is a group of organisms of the same species, all living in the same area and interacting with each
other. Since they live together in one area, members of the same species reproduce together. Ecologists who study
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populations figure out how healthy or stable the populations are. They also look at how the populations interact with
the environment.
First, ecologists will measure the size of the population. The population density is the number of individuals of
the same species in a particular area. Ecologists also look at how individuals in a population are spread across an
environment. How individuals are spaced within a population is called dispersion. Some species may be clumped
or clustered (Figure 23.4 ) in an area. Others may be evenly spaced (Figure 23.5 ). Still others may be spaced
randomly within an area.
FIGURE 23.4
Individuals within this population of purple loosestrife plants are clumped because of the soil quality.
FIGURE 23.5
A population of cacti in the Sonoran
Desert generally shows even dispersion
due to competition for water.
Ecologists also study age and sex. The birth rate is the number of births per individual within a specific time period.
The death rate is the number of deaths within a population during a specific time period. Knowing the birth and
death rates of populations gives you information about a population’s health. For example, when a population is
made up of mostly young organisms, it means that the population is growing.
A population with equal birth and death rates will have equal numbers of individuals at each age level. A population
with more individuals at or above an age when they can reproduce means that the number of individuals is decreasing
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in the population. This is because the organisms in this population cannot reproduce any more, so more children
cannot be born, and then the population cannot grow.
Births, Deaths, and Migration
Births, deaths and migration all affect population growth. The population growth rate tells you if the number of
individuals in a population is increasing or decreasing. Population growth rate depends on birth rate and on death
rate. You can predict the growth rate by using the simple equation below:
growth rate = birth rate – death rate.
If the birth rate is larger than the death rate, then the population grows. If the death rate is larger than the birth rate,
what will happen to the population? The population will go down. If the birth and death rates are equal, then the
population will stay the same.
Factors that affect reproduction are:
a.
b.
c.
d.
e.
f.
Age at first reproduction.
How often an organisms reproduces.
The number of offspring.
Parental care.
How long an organisms is able to reproduce.
Death rate of offspring.
Organisms can use different strategies to increase their reproduction rate. Altricial organisms are helpless at birth
and their parents give them a lot of care (Figure 23.6 ), while precocial organisms can take care of themselves at
birth and do not require help from their parents (Figure 23.7 ). In order to reproduce as much as possible, they use
very different strategies.
FIGURE 23.6
A hummingbird nest with young illustrates an altricial reproductive strategy
with a few small eggs helpless and
naked young and intensive parental
care.
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FIGURE 23.7
The Canada goose shows a precocial
reproductive strategy. It lays a large
number of large eggs producing welldeveloped young.
Migration
Migration is the movement of individual organisms into or out of a population. Migration affects population growth
rate. There are two types of migration:
a. Immigration is the movement of individuals into a population from other areas. This increases the population
growth rate.
b. Emigration is the movement of individuals out of a population. This decreases the population growth rate.
The earlier growth rate equation now looks like this:
growth rate = (birth rate + immigration rate) – (death rate + emigration rate)
One type of migration that you are probably familiar with is the migration of birds. Maybe you have heard that birds
fly south for the winter. In the fall, birds fly thousands of miles to the south where is warmer. In the spring, they
return to their homes. (Figure 23.8 ).
Monarch butterflies also migrate from Mexico to the northern U.S. in the summer and back to Mexico in the winter.
These types of migrations move entire populations from one location to another.
Population Growth
If a population is given unlimited amounts of food, moisture, and oxygen, and other environmental factors, it will
show a type of growth called exponential growth. Exponential growth means that as a population grows larger, the
growth rate increases. This is shown as the J-shaped curve in Figure 23.9 . You can see that the population grows
slowly at first, but as time passes, growth occurs more and more rapidly.
In nature, organisms do not usually have ideal environments with unlimited food. In nature, there are limits. Sometimes, there will be a lot of food. Sometimes, a fire will wipe out all of the available nutrients. Sometimes a predator
will kill many individuals in a population. How do you think these limits affect the way organisms grow?
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FIGURE 23.8
A flock of barnacle geese fly in formation during the autumn migration in Finland.
FIGURE 23.9
Growth of populations according to exponential or J − curve growth model
le f t and logistic or S − curve growth
model right
Usually, populations first grow exponentially. But as populations increase, rates of growth slow down and slowly
level off. This is shown as an S-shaped curve in Figure 23.9 , and is called logistic growth. Why do you think
occurs?
Limiting Factors
Limiting factors are things in the environment that can lower the population growth rate. Limiting factors include a
low food supply and lack of space. Limiting factors can lower birth rates, increase death rates, or lead to emigration.
When organisms face limiting factors, they show logistic type of growth (S-curve). Competition for resources like
food and space cause the growth rate to stop increasing, so the population levels off. This flat line in growth is
known as the carrying capacity. The carrying capacity is the maximum population size that can be supported in a
particular area without destroying the habitat. Limiting factors determine what the carrying capacity is.
Food Supply as Limiting Factor
If there are 12 hamburgers at a lunch table and 24 people sit down at a lunch table, will everyone be able to eat? At
first, maybe you will split hamburgers in half, but if more and more people keep coming to sit at the lunch table, you
will not be able to feed everyone. This is what happens in nature. But in nature, organisms that cannot get food will
die or find a new place to live.
In nature, when the population size is small, there is plenty of food for each individual. When there is plenty of food,
organisms can reproduce, so the birth rate is high. As the population increases, the food supply decreases. When
food decreases, organisms cannot reproduce as well, so the birth rates goes down. This will cause the population
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growth rate to decrease.
When the population decreases to a certain level where every individual can get enough food to eat, and the birth
and death rates are stable, the population has reached its carrying capacity.
Other Limiting Factors
Other limiting factors include light, water, nutrients or minerals, oxygen, the ability of an ecosystem to recycle
nutrients and/or waste, disease and/or parasites, temperature, space, and predation. Can you think of some other
factors that limit populations?
Weather is also a limiting factor. For example, an individual Agave americana actually likes to grow when it is dry.
Rainfall limits reproduction, which in turn limits growth rate. Can you think of some other factors like this?
Human activities can also limit the growth of populations. Such activities include use of pesticides, such as DDT,
use of herbicides, and habitat destruction.
What kind of growth rate do you think humans follow? Are they growing exponentially (J-curve) or logistically
(S-curve)?
Growth of the Human Population
There are two different beliefs about what type of growth the human population undergoes:
a. Neo-Malthusians believe that human population growth cannot continue without destroying the environment,
and maybe humans themselves.
b. Cornucopians believe that the Earth can give humans a limitless amount of resources. They also believe that
technology can solve problems caused by limited resources, such as lack of food.
Which do you think is correct?
Does human growth looks like the exponential (J-shaped) graph or the logistic (S-shaped) graph? We don’t know all
the answers yet, but history gives us some clues. For example, if we look at worldwide human population growth
from 10,000 BCE through today, our growth looks like exponential growth. It increases very slowly at first, but
later grows at a faster rate. It also does not approach a carrying capacity (Figure 23.10 ). So maybe humans show
exponential growth.
FIGURE 23.10
Worldwide human population growth
from 10 000 BCE through today
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On the other hand, if you look at human population growth in specific countries, you may see a different pattern. On
the level of a country, the history of human population growth can be divided into five stages, as described in Table
23.3 .
TABLE 23.3: Stage of Human Population Growth
Stage of Human Population Growth
Stage 1
Stage 2
Stage 3
Stage 4
Stage 5
Description
Birth and death rates are high and population growth is
stable. This occurred in early human history.
Significant drop in death rate, resulting in exponential
growth. This occurred in 18th and 19th century Europe.
Population size continues to grow.
Birth rates equal death rates and populations become
stable.
Total population size may level off.
The United Nations and the U.S. Census Bureau predict that by 2050, the Earth will be populated by 9.4 billion
people. Other estimates predict 10 to 11 billion.
The Cornucopians believe that a larger population is good for technology and innovation. The 5-stage model above
predicts that when all countries are industrialized, the human population will eventually reach a carrying capacity.
But many scientists and other Neo-Malthusians believe that humans have already gone over the Earth’s carrying
capacity for resources and habitat. If this is true, then human overpopulation will lead to a lack of food, disease, or
war. These things will cause the population of humans to crash, or cause humans to go extinct.
For additional information, see this 2010 video: http://whoknew.news.yahoo.com/?vid=21435088.
Which of the above theories makes sense to you? Why?
Lesson Summary
• A population is made of organisms belonging to the same species, all living in the same area and interacting
with each other
• One measure of a population’s health is the dispersion of individuals within a population
• The population growth rate shows how the population size changes per population member per unit of time.
• Birth rate, death rate, and migration affect population growth rate.
• In an ideal environment, populations show exponential growth. In nature, limiting factors cause logistic
growth.
• There are two major beliefs about human population growth. Neo-Malthusians believe that human population
growth is limited, and that overpopulation could have serious consequences. Cornucopians believe that human
population growth can continue because of natural resources and technology.
Review Questions
Recall
1. Name two ways ecologists know that a population is healthy.
2. Define Birth Rate.
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3. Define Death Rate.
4. What is the equation that calculates growth rate in a population, include information on migration?
5. What are three factors that affect reproduction within a population?
Apply Concepts
6. How does a limiting factor such as food supply limit population size?
7. Give two examples of environmental crises that support the idea that our human population has already grown
beyond the carrying capacity resulting in environmental degradation.
8. What is the difference between Neo-Malthusian beliefs and Cornucopian beliefs about human population growth?
Critical Thinking
9. In the altricial reproductive strategy used by robins and hummingbirds, the birds hatch helpless and naked. Parents
spend little energy in just a few small eggs. It is important these offspring survive because there are not very many
of them. What strategies might parents use to make sure their young survive?
10. In human history, major advances in technology caused our population to increase rapidly. What do you think
these major advances were?
Further Reading / Supplemental Links
•
•
•
•
http://www.brainpop.com/science/ourfragileenvironment/populationgrowth/preview.weml
http://eelink.net/pages/EE+Activities+-+Population
http://mathforum.org/t2t/faq/census.html
http://en.wikipedia.org/wiki/Population_ecology
Points to Consider
• Now that you understand what makes up a population, what do you think makes up a community?
• You have learned about some of the factors that limit populations. What do you think are some interactions
that affect the community?
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23.3
Communities
Lesson Objectives
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•
•
•
Define community.
Describe community interactions.
Explain how competition affects the community.
Describe predation and how it affects prey density.
Explain what symbiosis is and give examples of different kinds of symbiosis.
Check Your Understanding
• What is a population?
• How do limited resources encourage competition?
Vocabulary
camouflage An appearance which helps a species blend into the background.
character displacement Occurs when two or more species within the same area develop different specializations
in order to coexist.
commensalism type of symbiosis in which one species benefits while the other is not affected.
competition Organisms of the same or different species compete for a limited supply of at least one resource,
thereby lowering the fitness of one organism by the presence of the other.
competitive exclusion principle Species less suited to compete for resources will either adapt, be excluded from
the area, or die out.
keystone species A predator species that plays an important role in the community by controlling the prey population.
mutualism A type of symbiosis in which both species benefit.
parasitism A type of symbiosis in which the parasite species benefits, while the host species is harmed.
predation An interaction where a predator organism feeds on another living organism or organisms, known as
prey.
symbiosis Close and often long-term interactions between different species, in which at least one species benefits.
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What is a Community?
From populations, we are moving to the next level of ecology: the community level. In a community, different
species that live in the same area interact with each other. The term "community" can be used in different ways.
You can study populations in different areas of during different time periods. For example, you may study the fish
community in Lake Ontario. But you could also study fish in a lake during a particular time period, like after 1990.
Community Interactions
Community interactions can be either:
a. Intraspecific: Interactions between members of the same species.
b. Interspecific: Interactions between members of different species.
There are a number of different types of interactions, but we will look at three different types:
a. Competition.
b. Predation.
c. Symbiosis.
Competition
Competition occurs when organisms compete for limited resources, and the “fitness” of one individual is lowered
by competing with another individual. The interaction can be between organisms of the same species (intraspecific)
or different species (interspecific).
Intraspecific competition happens when members of the same species compete for the same resources. They can
compete for food, nutrients, space, or light. For example, two trees may grow close together and compete for light.
One may out-compete the other by growing taller to get more available light. The organism that is better adapted to
that environment gets to survive. In this case, it is the taller tree.
Interspecific competition happens when individuals of different species share a limited resource in the same area.
One species will have lowered reproductive success, growth, or survival. For example, cheetahs and lions feed on
similar prey. If prey is limited, then lions may catch more prey than cheetahs. This will force the cheetahs to either
leave the area or suffer a decrease in population.
Looking at different types of competition, ecologists developed the competitive exclusion principle. The principle
states that species less suited to compete for resources will either adapt, move from the area, or die out. This
is similar to what happens within a species. Evolutionary theory says that competition for resources within and
between species plays an important role in natural selection (Table 23.4 ).
In order for two species within the same area to adapt, they may develop different specializations in order to coexist.
This is known as character displacement. An example of character displacement is when different birds adapt to
eating different types of food. They can develop different types of bills, like Darwin’s Finches (Figure 23.11 ).
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FIGURE 23.11
An example of character displacement
showing different types of bill for eating different types of foods in Darwin&#8217 s or Galapagos Finches.
TABLE 23.4: Main Features of Competition
Type of Competition
Intraspecific Competition
Interspecific Competition
Description of Competition
Occurs when members of the same species compete for
the same resources, like food, nutrients, space, or light
Occurs when individuals of different species share a
limiting resource in the same area
Predation
Predation happens when a predator organism feeds on another living organism or organisms, known as prey. The
predator always lowers the prey’s fitness. It does this by keeping the prey from surviving, reproducing, or both.
There are different types of predation, including:
• True predation.
• Grazing.
• Parasitism.
True predation happens when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large
prey. They tear it apart and chew it before eating it (Figure 23.12 ). Others, like bottlenose dolphins or snakes, may
eat their prey whole. In some cases, the prey dies in the mouth or digestive system of the predator. Baleen whales,
for example, eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for
prey, or they may sit and wait for prey to get within striking distance.
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FIGURE 23.12
This example of a true predator shows
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example, if all of the wolves are removed from a population, then the population of deer may increase. If there are
too many deer, then they may decrease the amount of plants or grasses in the ecosystem.
The act of predation can be broken down into four stages:
a.
b.
c.
d.
Predator senses the prey.
Predator attacks the prey.
Predator captures the prey.
Predator eats the prey.
At each stage, predators have adaptations for getting the prey. Prey also have adaptations for avoiding predators.
(Table 23.5 ).
Prey sometimes avoid detection by using camouflage (Figure 23.13 ). Camouflage means that species have an
appearance (color, shape or pattern) that helps them blend into the background. Mimicry is a related adaptation
where a species uses appearance to copy another species. For example, a non-poisonous dart frog may evolve to
look like a poisonous dart frog. Why do you think this is an adaptation for the non-poisonous dart frog? Mimicry
can be used by both predators and prey (Figure 23.14 ).
TABLE 23.5: Main Features of Predation
Type of Predation
True Predation
Grazing
Description of Predation
Predator kills and eats its prey
Predator eats part of the prey, but rarely kills it
FIGURE 23.13
Camouflage by the dead leaf mantis
makes it less visible to both its predators and prey. If alarmed it lies motionless on the rainforest floor of Madagascar Africa camouflaged among the actual dead leaves. It eats other animals
up to the size of small lizards.
Symbiosis
Symbiosis describes a close and long-term interaction between different species. At least one species will benefit in
a symbiotic relationship. There are three types of symbiotic relationships:
a. Mutualism: Both species benefit.
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FIGURE 23.14
An example of Batesian mimicry where
the Viceroy butterfly right mimics the
unpalatable Monarch butterfly le f t .
Both species are avoided by predators
to a greater degree than either one
would be otherwise.
b. Commensalism: One species benefits while the other is not affected.
c. Parasitism: The parasitic species benefits, while the host species is harmed.
An example of a mutualistic relationship is between herbivores (plant-eaters) and the bacteria that live in their
intestines. The bacteria get a place to live while they also help the herbivore to digest food. Both species benefit, so
it is a mutualistic relationship.
The Ocellaris clownfish and the Ritteri sea anemones also have a mutualistic relationship. The clownfish protects the
anemone from anemone-eating fish, and the stinging tentacles of the anemone protect the clownfish from predators
(Figure 23.15 ).
Commensal relationships may involve an organism using another for transportation or housing. For example, spiders
build their webs on trees. The spider gets to live in the tree, but the tree is unaffected.
An example of a parasite is a hookworms. Hookworms live inside of humans and cause them pain, but the hookworms must live inside of a host in order to survive. Parasites may even kill the host they live on. Parasites are found
in animals, plants, and fungi.
FIGURE 23.15
A mutualistic relationship between the
Ocellaris clownfish and the Ritteri sea
anemone. Myako Island Japan. The fish
protects the anemone from anemoneeating fish while the anemone protects
the clownfish from its predators with its
stinging tentacles. The clownfish has a
special mucus which protects it from the
tentacles.
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Lesson Summary
•
•
•
•
•
•
•
A community is a collection of populations of different species interacting with one another in the same area.
Community interactions include competition, predation, and symbiosis.
Intraspecific and interspecific competition occur when individuals share a limiting resource in the same area.
The competitive exclusion principle plays an important role in natural selection.
Types of predation include true predation, grazing, and parasitism.
Prey use different adaptations to avoid detection, attack and capture by predators.
Symbiosis includes mutualism, commensalism, and parasitism.
Review Questions
Recall
1. Define competition.
2. What is the difference between intraspecific and interspecific competition?
3. Name three different types of predation.
4. In the mutualistic relationship between the Ocellaris clownfish and the Ritteri sea anemones, what benefit does
the fish get?
Apply Concepts
5. If two similar species do not live in the same area, would you expect the two species to compete? Why or why
not?
6. How might a predator lower a prey’s fitness?
7. In most types of grazing, does the predator lower a prey’s fitness? Why or why not?
8. A drone fly looks a lot like a bee, yet it is completely harmless, as it cannot sting at all. What anti-predator
mechanism is the drone fly using? Would you expect predators to always avoid drone flies?
Critical Thinking
9. Choose one of the symbiotic relationships: mutualism, parasitism, or commensalism. Think of an example of that
type of symbiosis. Explain why it is that type.
Further Reading / Supplemental Links
en.wikipedia.org/wiki/Symbiosis
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http://www.sciencenewsforkids.org/pages/search.asp
http://www.blm.gov/education/LearningLandscapes/students.html
http://www.nclark.net/CommunitiesBiomes
http://www.ecokidsonline.com/pub/index.cfm
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Points to Consider
• How do you think predation helps a species to survive?
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Ecosystems
Lesson Objectives
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Define ecosystem.
Discuss how biotic and abiotic factors play a role in ecosystems.
Explain what a niche is and its importance in an ecosystem.
Describe what a habitat is and how an organism is adapted to live in the habitat.
Check Your Understanding
• What is a community?
• What are the different types of community interactions?
Vocabulary
habitat Ecological or environmental area where a particular species live.
niche A specific role that an organism occupies within an ecosystem.
What is an Ecosystem?
The next level after community is an ecosystem. An ecosystem consists of all the biotic factors (plants, animals and
micro-organisms) interacting with all of the abiotic factors (water, soil, and air, for instance) in the same area.
You can find an ecosystem in a large body of freshwater or in a small piece of dead wood. Other examples of
ecosystems include the coral reef, the Greater Yellowstone ecosystem, the rainforest, the savanna, the tundra, the
desert and the urban ecosystem (Figure 23.16 ).
Ecosystems need energy. They mostly get their energy in the form of sunlight. Matter is also recycled in ecosystems.
Recycling of nutrients is important so they can always be available. Elements like carbon, nitrogen, and water are
used over and over again by organisms. Human ecosystems could be a household, neighborhood, college, or even a
nation. Human ecosystems interact with each other. Since humans live virtually all over the planet today, nearly all
ecosystems could be considered human ecosystems.
In 2005, the largest assessment ever conducted of the earth’s ecosystems was done by a research team of over 1,000
scientists. The study concluded that in the past 50 years, humans have altered the earth’s ecosystems more than any
other time in our history.
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FIGURE 23.16
An example of a desert ecosystem in
Baja California showing Saguaro cacti.
Biotic and Abiotic Factors
Biotic factors of an ecosystem include all living parts. Examples of biotic factors include bacteria, fungi, unicellular
and multicellular plants, and unicellular and multicellular animals.
Abiotic factors are non-living chemical and physical factors in the environment. The six major abiotic factors are
water, sunlight, oxygen, temperature, soil and climate (such as humidity, atmosphere, and wind). Other factors
include carbon dioxide, geography, and geology.
Abiotic and biotic factors interact within ecosystems and also between ecosystems. For example, water may be
recycled between ecosystems, by the means of a river or ocean current. Some species, such as salmon or freshwater
eels, move between marine and freshwater ecosystems.
Niche
Each organisms plays a particular role, or niche, in its ecosystem. A niche is the role a species or population plays
in the ecosystem. In other words, a niche is how an organism “makes a living.” A niche will include the food of an
organism and how it obtains its food and space. Different species can hold similar niches in different locations. The
same species may occupy different niches in different locations. Species of the Australian grasslands have the same
niche. Once a niche is left vacant, other organisms can fill that position. When the tarpan, a small, wild horse found
mainly in southern Russia, became extinct in the early 1900s, the niche was filled by a small horse breed, the konik
(Figure 23.17 ).
When plants and animals are introduced, either intentionally or by accident, into a new environment, they can occupy
new niches or the existing niches of native organisms. Sometimes new species out-compete native species. They
can even become a serious pest.
For example, kudzu, a Japanese vine, was planted in the southeastern United States in the 1870s to help control soil
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FIGURE 23.17
The konik horse which filled the niche
left by the tarpan a horse that became
extinct in the early 1900s in southern
Russia.
loss. Kudzu had no natural predators, so it was able to out-compete native species of vine and take over their niches
(Figure 23.18 ).
FIGURE 23.18
Kudzu a Japanese vine introduced intentionally to the southeastern United
States has out-competed the native
vegetation.
As discussed in the previous lesson, the competitive exclusion principle states that if niche overlap occurs, either one
species will be excluded, character displacement will happen (as in Darwin’s Finches), or the species will go extinct.
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Habitat
The habitat is the environmental area where a particular species lives (Figure 23.19 ). Abiotic factors are used to
describe a habitat. The average amount of sunlight received each day, the range of annual temperatures, and average
yearly rainfall can all describe a habitat. These and other factors will affect the kind of traits an organism must have
in order to survive there (Figure 23.20 and Figure 23.21 ).
FIGURE 23.19
Santa Cruz the largest of the northern
Channel Islands has the most diverse
of habitats in the sanctuary including a
coastline with steep cliffs coves gigantic caves and sandy beaches.
FIGURE 23.20
Another example of a type of habitat
showing a meadow and representative
vegetation.
Habitat destruction means what it sounds like - a species’ habitat is destroyed. Habitat destruction can cause a
species’ population to decrease. If bad enough, it can also cause species to go extinct. Clearing large areas of
land for housing developments or businesses can cause habitat destruction. Poor fire management, pest and weed
invasion, and storm damage can also destroy habitats.
National parks, nature reserves, and other protected areas all preserve habitats. The Environmental Problems chapter
will discuss habitat destruction in further detail.
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FIGURE 23.21
The above image shows wetland reeds
another type of habitat.
Habitats can also be examined from a human point of view. The environments where we live, work, and reproduce
are our habitats.
Lesson Summary
• An ecosystem consists of all the biotic and abiotic factors interacting together in an area.
• Biotic factors include all living components of an ecosystem. Abiotic factors are the non-living chemical and
physical factors in the environment.
• The niche concept is one of the most important ideas associated with ecosystems.
• If niche overlap occurs, then the competitive exclusion principle comes into play.
• The habitat is the area where a particular species, species population, or community lives.
• Habitat destruction is a major cause of population decrease, leading to possible extinction.
• Both the ecosystem and habitat can be looked at from a human point of view.
Review Questions
Recall
1. Give three examples of ecosystems.
2. List the six most common abiotic factors.
3. What is a niche?
4. Give an example of an organism filling a vacant niche.
5. What is a habitat?
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Apply Concepts
6. Why might a newly introduced species become a pest?
7. Name three abiotic factors that can be used to describe a habitat.
8. Give one example of an organism and its niche that is not included in the chapter.
Critical Thinking
9. Species that travel distances between important areas for their survival, like migrating birds, may be particularly
vulnerable to habitat destruction. How might the creation of multiple national parks or nature reserves help such
species?
Further Reading / Supplemental Links
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Unabridged Dictionary, Second Edition. Random House, New York, 1998.
http://www.kidsgeo.com/geography-for-kids/0164-ecosystems.php
http://www.kids-courier.com/kids-learning/science/science-terrestrial.html
http://www.bellmuseum.org/distancelearning/prairie/index.html
http://www.epals.com/projects/ducks_unlimited
http://www.fws.gov/endangered/kids/index.html
http://www.blm.gov/education/LearningLandscapes/students.html
http://en.wikipedia.org/wiki
Points to Consider
• Now that you understand what makes up an ecosystem, what additional factors do you think might be added
to get to the next level, the biome?
• How do you think what you have learned about abiotic and biotic factors might be applied to the classification
of different biomes?
• The biosphere is considered to be a global ecological system. Given all you now know about ecology, what
do you think the biosphere consists of?
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Biomes and the Biosphere
Lesson Objectives
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Explain what biomes are.
Describe terrestrial biomes.
Describe aquatic biomes.
Describe the features of the biosphere and list specific systems.
Check Your Understanding
• What is an ecosystem?
• How do ecosystems relate to humans?
Vocabulary
aquatic biomes Biomes divided into freshwater and marine biomes and defined according to different physical
and ecological factors.
elevation Measures how high land is above sea level.
GAIA hypothesis The concept that the biosphere is itself a living organism.
humidity The amount of water in the air.
latitude How far a biome is from the equator.
terrestrial biomes Biomes defined based on plant and climatic factors.
What are Biomes?
The biome is the highest level of organization in ecology. Biomes include populations, communities, and ecosystems. A biome is an area with similar geography and climate that includes similar communities of plants and
animals.
There are into two major groups of biomes:
a. Terrestrial biomes (land).
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b. Aquatic biomes (water).
Different biomes are habitats for different organisms. For example, one may find algae only in the part of the ocean
where there is light, while conifers may be mostly found in mountains.
The diversity of animals and plants that can live in a specific biome is determined by the abiotic factors. For example,
where there is more land, there are more species. Near the equator, there is also more biodiversity, probably because
there is more water caused by high humidity levels.
Biomes are classified in terms of two factors:
a. Latitude.
b. Humidity.
Using these two factors, the World Wildlife Fund (WWF) identified fourteen biomes. They then divided those 14
biomes into 825 terrestrial ecoregions.
Biomes are often given local names. For example, a "temperate grassland" biome is known as "steppe" in central
Asia, "prairie" in North America, and "pampas" in South America.
Terrestrial Biomes
Different terrestrial biomes are defined in terms of their plant structures (such as trees, shrubs, and grasses), leaf
types (such as broadleaf and needleleaf), and plant spacing (forest, woodland, savanna). Climate also affects what
type of terrestrial biomes will exist in a specific area. The following factors affect biome type:
• Latitude means how far a biome is from the equator. Moving from the poles to the equator, you will find
Arctic, boreal, temperate, subtropical, tropical biomes.
• Humidity is the amount of water in the air. Air with a high concentration of water will be called humid.
Moving away from the most humid climate, biomes will be called semi-humid, semi-arid, or arid (the driest).
• Elevation measures how high land is above sea level. Higher elevations have a similar affect on biomes as
increasing latitude.
This is summarized in Table 23.6 .
Terrestrial biomes (Figure 23.22 ) lying within the Arctic and Antarctic Circles do not have very much plant or
animal life. Biomes with the highest amount of diversity are near the equator (Figure 23.23 ).
TABLE 23.6: Characteristics of Terrestrial Biome
Characteristics of Terrestrial Biome
Plant structures
Leaf types
Plant spacing
Latitude from poles towards the equator
Humidity
Elevation
23.5. BIOMES AND THE BIOSPHERE
Description of Characteristics
Trees, shrubs, grasses
Broadleaf, needleleaf
Forest, woodland, savanna
Arctic, boreal, temperate, subtropical, tropical
Humid, semi-humid, semi-arid, arid
Increasing elevation causes habitat types similar to that
of increasing latitude
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FIGURE 23.22
One of the terrestrial biomes taiga is a
coniferous evergreen forest of the subarctic covering extensive areas of northern North America and Eurasia. This
taiga is along the Denali Highway in
Alaska. The Alaska Range is in the
background.
FIGURE 23.23
Another terrestrial biome is tropical rainforest. The one pictured here is located
in the Amazon basin north of Manaus
Brazil. The image was taken within 30
minutes of a rain event and a few white
clouds above the canopy are indicative
of rapid evaporation from wet leaves after the rain.
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Aquatic Biomes
Aquatic biomes can be defined according to:
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Size.
Depth.
Vegetation, such as a kelp forest.
Animal communities.
According to the WWF scheme, freshwater biomes can be classified as the following:
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Large lakes (Figure 23.26 ).
Large river deltas.
Polar freshwaters.
Montane freshwaters (in mountain areas).
Temperate coastal rivers.
Temperate floodplain rivers and wetlands.
Temperate upland rivers.
Tropical and subtropical coastal rivers.
Tropical and subtropical floodplain rivers and wetlands.
Tropical and subtropical upland rivers.
Xeric (dry habitat) freshwaters and endorheic (interior drainage) basins.
Oceanic islands.
The WWF classifies marine (salt or ocean water) biomes according to:
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Polar habitat types.
Temperate seas.
Temperate upwelling.
Tropical upwelling.
Tropical coral.
Other marine habitat types include:
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Continental shelf.
Littoral/intertidal zone.
Coral reef.
Kelp forest (Figure 23.24 ).
Pack ice (Figure 23.25 ).
Hydrothermal vents.
Cold seeps.
Benthic zone.
Pelagic zone.
Neritic zone.
The Biosphere
The highest level of ecology is the biosphere. It is the part of the Earth, including the air, land, surface rocks, and
water, where you can find life.
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FIGURE 23.24
An example of an aquatic marine biome
a kelp forest located near Santa Cruz
Island Channel Islands National Park
California.
FIGURE 23.25
An example of an aquatic marine biome
pack ice.
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FIGURE 23.26
Lake Tahoe in Northern California is a
freshwater biome.
The biosphere interacts with the:
• Lithosphere: sphere of soils and rocks.
• Hydrosphere: water.
• Atmosphere: air.
The biosphere includes an area between 11,000 meters below sea level to 15,000 meters above sea level. It overlaps
with the above three spheres.
The GAIA hypothesis states that the biosphere is its own living organism. The hypothesis explains how biotic and
abiotic factors interact in the biosphere.
The atmosphere, hydrosphere and lithosphere are cooperating systems that produce a biosphere full of life.
Lynn Margulis, a microbiologist, added to the hypothesis, specifically noting the ties between the biosphere and other
Earth systems. For example, when carbon dioxide levels increase in the atmosphere, plants grow more quickly. As
their growth continues, they remove more carbon dioxide from the atmosphere.
For a better understanding of how the biosphere works and various dysfunctions related to human activity, scientists
have simulated the biosphere in small-scale models. Biosphere 2 (Figure 23.27 ) is a laboratory in Arizona that
contains 3.15 acres of closed ecosystem. BIOS-3 was a closed ecosystem in Siberia, and Biosphere J is located in
Japan.
Direct human interactions with ecosystems, including agriculture, city development and other land uses, affect the
health of the biosphere and their ecosystems. In terms of the human impact on biomes and ecosystems, the study
of ecology is now more important than ever. Scientists that study ecology will move us toward an understanding of
how best to live in and manage our biosphere.
Lesson Summary
• A biome is an area with similar geography and climate that contains ecologically similar communities of
plants and animals.
• Biomes are classified in different ways, sometimes according to differences in the physical environment, and
sometimes according to latitude and humidity.
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FIGURE 23.27
Biosphere 2 in Arizona contains 3.15
acres of closed ecosystem and is a
small-scale model of the biosphere.
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Biodiversity of each biome is determined by abiotic factors, such as water and temperature.
Terrestrial biomes are classified based on various plant factors and on climate.
Aquatic biomes are classified based on various factors and divided into freshwater and marine biomes.
The biosphere is a global ecological system.
The biosphere is itself a living organism, as explained by the GAIA hypothesis.
Humans have changed global patterns of biodiversity and ecosystem processes.
Review Questions
Recall
1. Define biome.
2. What is the difference between a terrestrial and an aquatic biome?
3. Name a type of biome based on the physical environment.
4. Name the aquatic biomes classified according to depth.
5. What is the GAIA hypothesis?
Apply Concepts
6. Where would you expect to find more biodiversity, in a rainforest on the equator, or in a desert? Explain why.
7. As you climb a mountain, you will see the vegetation a habitat type change as you gain elevation. What kind of
change will result in a similar change in habitat?
8. Name one way that human activity has affected the biosphere (maybe you have heard something on the news?)
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Critical Thinking
9. Water is recycled between the hydrosphere, lithosphere, atmosphere, and biosphere in regular cycles. Why do
you think oceans are important for this type of water recycling?
Further Reading / Supplemental Links
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http://www.kidsconnect.com/content/view/62/27
http://library.thinkquest.org/11353/ecosystems.htm
http://lsb.syr.edu/projects/cyberzoo/biome.html
http://earthobservatory.nasa.gov/Laboratory/Biome
http://www.worldbiomes.com/biomes_map.htm
http://www.mbgnet.net/sets/index.htm
http://www.mbgnet.net/fresh/index.htm
http://www.mbgnet.net/salt/index.htm
http://www.kidsgeo.com/geography-for-kids/0153-biosphere.php
http://www.geography4kids.com/files/land_intro.html
Points to Consider
You now have a general idea of what a biome is and how the diversity of a biome is related to other factors. The next
chapter, on ecosystem dynamics, will give you a greater understanding of how energy flow, cycling of matter, and
succession vary from one biome to another.
• One of the aquatic biomes, the hydrothermal vents, is not dependent on sunlight but on bacteria, which utilize
the chemistry of the hot volcanic vents. Can guess where these bacteria fit into the flow of energy in such an
ecosystem?
23.5. BIOMES AND THE BIOSPHERE